It is known that a fine particle of metal (particle diameter of not larger than 1 μm) has a variety of specific characteristics which a bulk material does not have. Currently, the fine particle is greatly expected on a variety of technological applications with making the best use of such the characteristics, in individual fields, such as electronics, bio, energy, or the like.
Regarding a method for producing such the fine particle of metal having a nanometer size, it is known that there are two producing methods, i.e., a vapor phase synthesis method and a liquid phase synthesis method. The vapor phase synthesis method is a method to form a fine particle of metal as a solid state from a metal vapor introduced into a vapor phase. The liquid phase synthesis method is a method to precipitate a fine particle of metal by reducing a metal ion dispersed into a solution. In the liquid phase synthesis method, it is known in general that there are two methods, i.e., a method with using a reducing agent for reducing such the metal ion and a method to perform a reduction electrochemically on a cathode electrode.
The fine particle dispersion, in which the fine particles are dispersed into an aqueous solution or an organic solvent, is widely used for an application such as ink-jet ink, an etching resist, a solder resist, a dielectric substance pattern, an electrode (electrically conductive circuit) pattern, a wiring pattern in an electronic component, an electrically conductive paste, an electrically conductive ink, an electrically conductive film, or the like.
In recent years, an attention is focused on a technology that a wiring pattern is formed using an ink-jet method with ink containing a fine particle of metal and then a wiring is formed by baking thereof. However, in a case of using the ink containing the fine particle of metal for the ink-jet, it is important to retain dispersibility in the ink for a long period of time. Accordingly, a method for producing a fine particle of metal is proposed to retain the dispersibility for a long period of time in the ink.
Moreover, a method for producing a metal fine particle dispersion and a method for obtaining a metallic thin film or a thin metallic wire include a step of coating such the metal fine dispersion, and then baking after drying thereof, and are disclosed in patent documents as mentioned below.
According to patent document 1, regarding a method for obtaining a fine particle of copper, there is disclosed an electrically conductive thin film of copper to be formed by forming a fine particle of copper having a particle diameter of not larger than 50 nm containing palladium in a polyethylene glycol solution or an ethylene glycol solution by adding a palladium ion for nucleation with adding polyethyleneimine as a dispersing agent, by performing a pattern print onto a substrate using such the copper fine particle dispersion after a solvent displacement to ethanol and ethyl lactate, and then by performing a heat treatment therefor in an atmospheric current of 4% H2—N2 for approximately three hours at a temperature of 250° C.
According to patent document 2, there is disclosed ink for ink-jet by collecting a fine particle of cuprous oxide using a centrifugal separator, which has a primary particle diameter of not larger than 100 nm and is obtained by reducing with heating copper acetate in diethylene glycol, and then by re-dispersing it into a mixed solution comprised of polyethylene glycol and diethylene glycol, and disclosed a pattern of a metal wiring to be obtained by coating it onto a substrate using such the ink-jet method, and then by performing a reduction of cuprous oxide by performing a heat treatment therefor in nitrogen gaseous atmosphere for approximately one hour at a temperature of 350° C.
According to patent document 3, there is disclosed a thin film of silver by coating a nano particle of metal onto a substrate (a glass) using a spin coat method, on which an organic metal compound as a dispersing agent is attached to around the metal, by drying it at a temperature of 100° C., and then by baking it at a temperature of 250° C.
Furthermore, according to patent document 4, there is disclosed a thin film of copper by concentrating cuprous oxide for becoming to be a concentration of 30% by weight, which is suspended into diethylehe glycol, in which secondary particles have a mean particle diameter of 500 nm, by performing further a ultrasonic wave treatment therefor to be an electrically conductive ink, by coating it onto a slide glass, and then by heating it in a reducing atmosphere for approximately one hour at a temperature of 350° C.
[Patent Document 1] Japanese Patent Application Publication No. 2005-330552
[Patent Document 2] Japanese Patent Application Publication No. 2004-277627
[Patent Document 3] Japanese Patent Application Publication No. 2005-081501
[Patent Document 4] Japanese Patent Application Publication No. 2004-323568